Carbohydrate and metabonomic studies by NMR spectroscopy

Sammanfattning: NMR spectroscopy can be used to investigate organic and biomolecular structures, both as pure compounds and in complex mixtures. In this thesis NMR spectroscopy was used for carbohydrate and metabonomic studies. Lipopolysaccharides are major components of the outer cell membrane of Gram-negative bacteria and are involved in pathogenic interactions. The structure of a lipopolysaccharide from the human pathogen Plesiomonas shigelloides was analyzed by NMR spectroscopy and mass spectrometry. The structure contained an O-specific polysaccharide with a tetrasaccharide repeating unit. The core oligosaccharide was an undecasaccharide with previously not reported heterogeneity within the carbohydrate backbone. Hyaluronan is a glycosaminoglycan with high viscosity and water-retaining ability. Hydroxy protons of hyaluronan oligosaccharides were studied by NMR spectroscopy in aqueous solution to investigate hydrogen bonding interactions and hydration. Weak hydrogen bonding was observed between hydroxy protons and the ring oxygens over the β(1→3) and β(1→4) glycosidic linkages. A chemical exchange interaction was also identified between O(4)H of N-acetylglucosamine and O(3)H of glucuronic acid across the β(1→3) linkage. The interaction could be mediated through water bridges and thus contribute to the water-retaining ability of hyaluronan. Polyunsaturated fatty acids are essential nutritional components of marine lipid sources. A ¹H HR-MAS NMR method was developed to determine the amount of essential polyunsaturated fatty acids in fish muscle without any pretreatment. Additionally, the small metabolite profile of the fish muscle was obtained, which can be used to determine fish quality. Caloric restriction is known to increase the lifespan of rats. In order to evaluate the metabolic responses to graded caloric restriction in rats, blood serum was analyzed by NMR spectroscopy. Multivariate analysis showed a decrease in blood lipids and alanine, and an increase in creatine and 3-hydroxybutyrate as a response to caloric restriction.

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